This invention relates generally to feed hoppers for particulate material and more particularly to a feed hopper assembly for elastroscopic/magnetic toner powder used in the printing cycle of an electrostatic printer.
Electrostatic printers utilize a toner powder to identify the electrostatic image on a charged carrier as it goes through the printing cycle. The toner powder is fed through suitable outlet ports or openings for the feed hopper in which the toner is stored until required for this purpose, the toner being delivered onto a magnetic roller which in turn deposits the toner powder on the imaged carrier.
It is well known to those skilled in the art that toner powders by the nature of their particle shape, size and electrostatic properties have a tendency to agglomerate rather than to flow freely from the outlet ports or openings provided in the feed hopper from which the toner powder is dispensed. Where this agglomeration occurs, it produces erratic feeding of the toner to the magnetic applicator which in turn causes either variable image density or no image at all on the imaged carrier.
Various devices have been utilized to overcome this problem which momentarily break up the agglomerated particles so as to permit them to flow freely onto the applicator such as, mechanical stirrers, mechanical vibrators, and other techniques as shown for example in U.S. Pat. Nos. 3,900,002, 3,870,017 and 3,752,576.
However these prior art structures and devices have the disadvantage of frequently causing a greater degree of particle agglomeration or of causing adhesion of the powder either to the hopper walls or the stirring apparatus. In the case of vibrating devices, the entire mass of powder may be densified into a coherent nonflowing mass which further compounds the problem.
The present invention provides an improved feed hopper assembly for overcoming this problem in which an expansible device such as an elastomeric diaphragm on the inner wall of the storage chamber for the feed hopper thereof will gently pulsate the toner or like type of particulate material in the storage chamber so as to reduce agglomeration of the particles and thus enable the toner or other particulate material to flow freely from the discharge outlet or opening for the feed hopper.